JPH02119641A - Valve system of engine - Google Patents

Abstract

PURPOSE:To improve the combustibility of an engine by providing either of an intake and an exhaust valve of an engine with a supercharger with a timing mechanism for varying valve phase, and controlling its function so that the overlapping period of the intake and the exhaust valve may become longer under a heavy load and shorter under a light load. CONSTITUTION:In a valve system having cam shafts 18, 19 on an intake and an exhaust side, the cam shaft 19 on the exhaust side is axially divided near a timing pulley 23 into a cam shaft 19a on a driving side and a cam shaft 19b on a driven side, and the above-divided part of the cam shaft 19 is provided with a timing mechanism 28 for varying valve phase. The mechanism 28 is formed with spiral splines 24, 25 rotating in different directions on the periphery of the opposite ends of the divided cam shafts 19a, 19b, and a sleeve 26 driven by a stepping motor 27 is fitted on the splines 24, 25 with splines formed on the inside periphery of the sleeve 26 engaging with the splines 24, 25. The stepping motor 27 controls the valves so that overlapping period of the intake and the exhaust valve may become longer under a heavy load and shorter under a light load.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a valve train for an engine equipped with a supercharger.

(Prior Art) Conventionally, as disclosed in, for example, Japanese Unexamined Patent Publication No. 62-87615, a supercharger is provided in the intake passage of an engine,
Supercharged engines are widely known in which the output torque of the engine is increased by supercharging intake air through the operation of a supercharger and increasing the amount of intake air charged into the cylinder.

In an engine equipped with a supercharger as described above, when the supercharging pressure increases under high load or high rotation conditions,
As the final compression ratio becomes higher, knocking becomes more likely to occur, and to avoid this knocking, the compression ratio of the engine itself is set low. However, this reduction in compression ratio leads to deterioration in combustibility in a low load range where boost pressure is low.

Regarding the above point, by setting a large overlap period between the opening timings of the intake valve and exhaust valve, the high supercharging pressure of the intake air supercharged in the high load range is utilized, and the supercharged intake air is The high-temperature residual exhaust gas in the combustion chamber in the cylinder is pushed out to the exhaust side to enhance the scavenging effect, suppress the rise in intake compression temperature caused by the residual exhaust gas, and raise the knocking limit, and set a high intake compression ratio to improve fuel efficiency. It is possible to improve the

(Problem to be Solved by the Invention) However, if the overlapping period of the opening timings of the intake valve and exhaust valve is set large as described above to prevent knocking in the high load range, There is a problem that combustion stability decreases in the region.

In other words, in the low load range, the compression ratio increases due to the above-mentioned knocking measures, but since the overlap period is long and the boost pressure is low, the scavenging effect cannot be obtained as the intake negative pressure increases in this low load range. The exhaust gas is blown back into the intake passage, and the blown back exhaust gas flows directly into the combustion chamber, increasing the amount of residual exhaust gas and reducing combustibility.

Therefore, in view of the above points, the present invention installs a phase variable valve timing mechanism that changes the opening/closing timing of the intake valve or exhaust valve to prevent knocking at high loads and to ensure combustion stability at low loads. The object of the present invention is to provide a valve train for an engine that has the following characteristics.

(Means for Solving the Problems) In order to achieve the above object, a valve train for an engine according to the present invention includes a supercharger and a phase shifter that changes the phase of the opening/closing timing of either the intake valve or the exhaust valve. A variable valve timing mechanism is provided, and a control means is further provided for controlling the operation of the variable phase valve timing mechanism so that the overlap period between the intake valve and the exhaust valve is large at high loads and small at low loads. It is something.

(Function) In the above-mentioned valve train, when the load is high, the phase variable valve timing mechanism increases the overlap period, increases the scavenging effect due to the increased supercharging pressure, reduces residual exhaust gas, and reduces the amount of exhaust gas brought in. While reducing the amount of heat to suppress the occurrence of knocking and increasing the compression ratio, at low loads, the variable phase valve timing mechanism reduces the overlap period, reduces the intake of exhaust gas, and ensures combustion stability. There is.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 and FIG. 2 show a schematic configuration of a valve train for an engine in one embodiment.

The engine body 1 includes a cylinder block 2 and a cylinder head 3, and the cylinder block 2 is formed with a cylinder 5 into which a piston 4 is reciprocatably inserted. On the other hand, the cylinder head 3 is formed with an intake port 8 and an exhaust port 9 that communicate with the cylinder 5, and the intake and exhaust ports 8 and 9 are connected to an intake valve 6 and an exhaust valve 7, respectively.
It is opened and closed by

The intake port 8 constitutes a downstream end of an intake passage 10, and an upstream end of this intake passage 10 is connected to an air cleaner 11. In the middle of the intake passage 10, in order from the upstream side, there is an air flow meter 12 that detects the intake air port,
a throttle valve 13 that throttles and opens and closes the intake passage 10;
A mechanical supercharger 14 that is driven by the engine 1 and supercharges intake air, and a surge tank are provided, and the supercharger 1
The intake passages 10 immediately upstream and downstream of No. 4 are connected by a bypass passage 15 that relieves the intake air supercharged by the supercharger 14 to the upstream side of the supercharger 14, and this bypass passage 15 has an intake air relief amount. A bypass relief control valve 16 is provided for controlling. 17 is an injector that injects and supplies fuel into the intake port 8.

The intake and exhaust valves 6.7 are respectively driven open and closed by cams 20.21 on the shafts 18.19. The camshaft 18, 19 is connected to the cylinder head 3
The engine 1 is rotatably supported by a crankshaft (not shown) of the engine 1 via timing pulleys 22 and 23 attached to one end thereof and a timing belt (not shown) wrapped around the pulleys 22 and 23. Ru. The exhaust side camshaft 19 is separated into a driving side shaft 19a and a driven side shaft 19b in the axial direction near the timing pulley 23. A helical spline 24.25 is formed, and a sleeve 26 driven by a stepping motor 27 is slidable in the axial direction by a spline (not shown) on the inner circumference of the spline 24.25. By moving the sleeve 26 in the axial direction by the stepping motor 27, the drive side shaft 19a
By rotating the driven shaft 19b relative to the
A variable phase valve timing mechanism 28 is configured to change the phase of the opening/closing timing of the exhaust valve 7.

The operation of the stepping motor 27 that drives the sleeve 26 is controlled by a control unit 30 having a built-in CPU. This control unit 3
Signals from a rotation sensor 31 that detects the rotational speed of the engine 1 and a load sensor 32 as a load detection means that detects the engine load based on the amount of intake air and the like are input to 0.

In the control unit 30, advance control of the opening/closing timing of the exhaust valve 7 is performed using the following control procedure. That is, first, the engine speed detected by the rotation sensor 31 and the engine load detected by the load sensor 32 are respectively input, and the phase of the opening/closing timing of the exhaust valve 7 is set based on a preset map. , stepper motor 2 at this set phase
7.

As illustrated in FIG. 3, the above map divides the operating region of the engine 1 into a low speed, low load region (■), that is, an idle region, and another region I including a high speed, high load region.
In the high-speed, high-load region I, as shown in FIG. 4A, the phase of the opening and closing timing of the exhaust valve 7 is delayed, and the overlap period from the opening time 10 of the intake valve 6 to the closing time EC of the exhaust valve 7 is delayed. θ. and this overlap period θ. , the top dead center TDC of the piston 4
The period θ2 from EC to the closing time EC of the exhaust valve 7 is set to be longer than the period θ1 from the opening time 10 of the intake valve 6 to the top dead center TDC (θ2>θ1). on the other hand,
In the idle region (2), as shown in FIG. 4B, the phase of the exhaust valve 7 is changed to the advanced side from the opening/closing timing of the above-mentioned high-speed, high-load region I, and the exhaust valve 7 is closed from 10 when the intake valve 6 is opened. Overlap period θ until valve time EC.

is made smaller.

As shown by the broken line in FIG. 3, regardless of the engine speed, the overlap period θ0 is increased only in the high load region 1', and the overlap period θ is increased in the light load region 2' below that. may be set to be smaller.

To explain the operation of the above embodiment, the engine speed is detected by the rotation sensor 31 and the engine load is detected by the load sensor 32, and the control unit 30 adjusts the opening/closing timing of the exhaust valve 7 based on the engine speed and load. The phase is set, and the operation of the stepping motor 27 of the variable phase valve timing mechanism 28 is controlled so that the phase is set, and the opening/closing timing of the exhaust valve 7 is changed.

In the high load region of the engine 1, the phase of the opening/closing timing of the exhaust valve 7 is delayed (FIG. 4A) to provide an overlap period θ with the opening period of the intake valve 6. Increase the
The supercharger 14 can effectively push out the residual exhaust gas in the cylinder 5 to the exhaust port 9, increasing the scavenging effect, lowering the compression temperature, and preventing knocking.

In addition, when the load is low, the phase of the opening/closing timing of the exhaust valve 7 is advanced (FIG. 4B), and the overlap period θ is set so that the exhaust valve 7 is closed at an early stage. This is to reduce the amount of residual exhaust gas by suppressing the blowback of intake air, thereby achieving combustion stability.

In this case, under high load, the period θ2 from top dead center TDC to EC when exhaust valve 7 is closed is the period θ2 from IO when intake valve 6 is open to top dead center TDC! The overlap period θ0 is set to be longer than (θ2>θ1).
is set to be large, and the phase of the exhaust valve 7 is advanced during low load to obtain an overlap period θ. To suppress an increase in the amount of residual exhaust gas due to the opening time 10 of the intake valve 6 being too early when the time 10 is shortened. That is, if the above conditions are not met, the intake valve 6 will open too quickly at low load, and a large amount of combustion gas will be blown back to the intake side, increasing the amount of residual exhaust gas.

In the above embodiment, the phase of the opening/closing timing of the exhaust valve 7 is made variable, and the overlap period θ is set relative to the opening/closing timing of the intake valve 6 whose opening/closing timing is fixed. The phase variable valve timing mechanism 28 is installed on the intake side camshaft 18 to change the phase of the opening/closing timing of the intake valve 6 to control the overlap period θ. may be controlled so that it is large when the load is high and small when the load is low.

The overlap period θ is caused by varying the phase of the opening/closing timing of the intake valve 6. For example, as shown in FIG. 5A in a high load state, the phase of the opening/closing timing of the intake valve 6 is advanced to advance the intake valve opening time 10, and the exhaust valve 7 is
The overlap period θ0 up to the valve closing time EC is lengthened. In addition, when the load is low, as shown in Figure B, the phase of the opening/closing timing of the intake valve 6 is delayed and
is delayed to reduce the overlap period θ0 until the closing time EC of the exhaust valve 7.

In addition, in a high load state, the overlap period θ. It is preferable to set the period θl from the intake valve opening time 10 to the top dead center TDC to be longer than the period θ2 from the top dead center TDC to the exhaust valve closing time EC.

phase variable control of opening/closing timing of the exhaust valve 7;
Phase variable control of the opening/closing timing of the intake valve 6
There are some differences in functionality as follows.

First, in the phase variable control of the exhaust valve 7, the intake valve 6
The opening/closing timing of the valve is set widely in order to increase the intake efficiency, and it is set at a predetermined time before the top dead center TDC so that the opening time of 10 is too early and the intake air blowback is not excessive.
In addition, in order to prevent the intake valve closing IC from becoming too slow and shortening the effective compression period, the IC is fixed at a predetermined time after bottom dead center BDC, whereas the exhaust valve closing EC is delayed in a retarded state at high loads. to lengthen the overlap period θ0, and advance the exhaust valve closing EC in a low load state to set the overlap period θ. will be reduced. If this exhaust valve closes EC, if it is too early, the exhaust efficiency will decrease, if it is too late, the intake will be obstructed. Time EO is bottom dead center B from the point of view of exhaust efficiency
It is set to open at a time that is not too late before DC, but when the opening/closing timing is advanced to reduce the overlap period θ0 at low load, the exhaust valve opening E
If O becomes too rapid, the effective expansion period will be shortened, and the energy of the exhaust gas will be exhausted without being effectively utilized.

In addition, in the phase variable control of the intake valve 6, the exhaust valve 7
The opening/closing timing of the valve is set widely in order to increase exhaust efficiency, and the opening EO is set at a predetermined time before the bottom dead center BDC so that the effective expansion period is not shortened due to being too early.
The EC when the exhaust valve closes is too slow and is fixed after the top dead center TDC so as not to obstruct the intake, but when the intake valve opens during high load, ■ 0 is made earlier and the overlap period θ is set.

is made longer, and the overlap period θ is retarded by 10 when the intake valve opens under low load conditions. will be reduced.

The intake valve opening time 10 is set at a predetermined time before the top dead center TDC so as not to cause an excessive blowback of the intake air due to being too early, or to prevent the intake efficiency from decreasing due to being too late. From the point of view of intake efficiency, the IC is set to open not too early after bottom dead center BDC, but when the opening/closing timing is delayed to reduce the overlap period θ0 at low loads, If the IC closes too late, the effective compression period will be shortened, and the compression pressure and temperature will not rise, resulting in lower combustion efficiency. On the other hand, if the intake valve closing IC is advanced too early under high load, compression will actually start earlier, increasing the effective compression ratio, making knocking more likely to occur, and causing abnormal high-speed combustion. A problem arises.

As mentioned above, whether to change the overlap period θ0 by varying the phase of the exhaust valve 7 or by varying the phase of the intake valve 6 depends on the optimal setting of the opening/closing timing on the fixed setting side and the relationship between the respective phase change ranges. Both methods have advantages and disadvantages, and which one to choose should be determined according to various requirements.

On the other hand, when the load is high, the difference between the boost pressure and the exhaust pressure decreases as the rotation speed increases, and the overlap period θ0
The time during which the overlap period θ0 is changed becomes shorter as the engine speed increases, and the scavenging effect decreases. Therefore, it is recommended to change the overlap period θ0 according to the load as described above, and at the same time change it according to the engine speed. It may be set to That is, phase control may be performed so that the overlap period θ0 is lengthened as the engine speed increases.

Examples of this control are shown in FIGS. 6A-C. FIG. 6A shows that in a low speed light load region such as an idle state, the relatively small overlap period θ0 is controlled to increase sequentially as the engine speed and load increase;
In other non-idle regions, the overlap period θ increases as the engine speed increases. This is an example of increasing . As a result, even in the light load region, the effect of reducing NOx by internal EGR which increases the residual exhaust gas due to the relatively large overlap period θ0, and reducing the pumping loss by utilizing the heat amount of the exhaust gas and increasing the volume ratio is obtained. In addition, the overlap period θ is in the low speed and light load range. to ensure combustion stability.

Further, in FIG. 6B, the overlap period θ0 is gradually increased as the engine speed increases in the non-idle region, but the overlap period θ becomes larger as the load increases. This is an example in which the settings are made to reduce the . This further increases residual exhaust gas under light load conditions, thereby improving the heat utilization and pumping loss reduction effects.

Furthermore, in FIG. 6C, the overlap period θ changes as the engine speed increases only in the high load region. This is an example of setting to increase the value.

Furthermore, when the engine speed increases under full load,
In the case of an engine in which the exhaust pressure is higher than the boost pressure, the overlap period θ0 is
If the rotation speed is increased, the scavenging effect cannot be obtained and the residual exhaust gas increases, so in the region where the rotation speed exceeds the above, the overlap period θ0 may be set to be further reduced than when the load is low. .

In the above embodiments, a mechanical supercharger was used as the supercharger, but the present invention is also applicable to a turbo supercharger.

(Effects of the Invention) According to the present invention as described above, a supercharger for supercharging intake air is provided, and a variable valve timing mechanism for changing the opening/closing timing phase of either the intake valve or the exhaust valve is provided. By controlling the intake/exhaust overlap period to be larger at high loads and smaller at low loads, the increased boost pressure increases the scavenging effect and reduces residual exhaust gas at high loads. By reducing the amount of heat brought in by the exhaust gas, it is possible to suppress the occurrence of knocking and increase the compression ratio, ensuring the compression ratio in the region of low boost pressure and improving combustibility. In some cases, combustion stability can be ensured by reducing the amount of exhaust gas brought in with a small overlap period.

Furthermore, the above overlap period can be changed easily and at low cost by installing a variable phase valve timing mechanism that changes the opening/closing timing phase of either the intake or exhaust valve. It is.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an engine valve train according to an embodiment of the present invention, Fig. 2 is a plan view showing a schematic configuration of a variable phase valve timing mechanism, and Fig. 3 is a change in the overlap period of intake and exhaust valves. Characteristic diagrams showing the control region; Figures 4A and B are valve opening diagrams showing examples of phase changes in the opening and closing timing of exhaust valves according to the engine operating conditions; Figures 5A and B are valve opening diagrams showing examples of phase changes in the opening and closing timing of the exhaust valve according to the engine operating conditions. Figures 6A to 6C are valve opening diagrams showing examples of phase changes in intake valve opening/closing timing, and Figures 6A to 6C show control characteristics when controlling to change the overlap period of intake/exhaust and air valves in response to changes in engine speed. It is a characteristic diagram which each illustrates. 1...Engine, 4...Piston, 5
...Cylinder, 6...Intake valve, 7...
...Exhaust valve, 8...Intake boat, 9.
...Exhaust port, 14...Supercharger, 28
...... Phase variable valve timing mechanism, 30...
...Control unit (control means), 32...
...Load sensor, θ0...Overlap period. (B) 0C

Claims (1)

[Claims] (1) In an engine equipped with a supercharger, a variable phase valve timing mechanism is installed to change the phase of the opening/closing timing of either the intake valve or the exhaust valve, and the overlap period between the intake valve and exhaust valve is high. A valve operating system for an engine, characterized in that a control means is provided for controlling the operation of the variable phase valve timing mechanism so that the valve timing mechanism is large when loaded and small when the load is low.